Chapter 5 - The Central Nervous System

Question 1

What are the three main structures that protect the CNS?

Answer 1

• Bone
• Membranes called meninges
• A fluid called cerebrospinal fluid (CSF)

Question 2

Explain the bone protective layer of the CNS

Answer 2

The outermost protective layer of the CNS is bone.
The brain is protected by the cranium.
The part of the skull that the the vertebrae runs through is called the vertebral canal.

Question 3

What is the vertebral canal?

Answer 3

An opening in the cranium in which the spinal cord runs through.

Question 4

Explain the protective layers of meninges.

Answer 4

Inside the bones, and covering the surface of the brain and spinal cord are three layers of connective tissue that forms membranes called the meninges. They cover the entire CNS.
The outer membrane = tough and fibrous
The middle membrane = a loose mesh of fibres
The inner membrane = very delicate
The outer meningeal layer sticks closely to the bones of the skull, but the inside membranes are not so close fitting.

Question 5

Explain the protective structure of cerebrospinal fluid (CSF)

Answer 5

The CSF is in between the middle and inner layers of the meninges. It is a clear, watery fluid containing a few cells and some glucose, protein, urea and salts. It acts as a shock absorber, cushioning any blows or shocks to the head.
The CSF is formed from the blood and it circulated around and through the CNS, eventually re-entering the blood capillaries. It also takes nutrients to the cells of the brain and takes wastes away. Therefore the CSF protects, supports and aids in transport of the CNS.

Question 6

Explain the structure of the Cerebrum

Answer 6

The cerebrum is the biggest part of the brain. It consists of 2-4mm thick outer surface of grey matter known as the cerebral cortex. Below the cortex is white matter and deep inside the cerebrum is additional grey matter called the basal ganglia .

Question 7

What is the cerebral cortex? (Hint = gyri, sulci and fissures).

Answer 7

The cerebral cortex is the outer surface of the cerebrum. It is folded in patterns that increase its surface area. Because of this, the cortex contains 70% of all neurons in the CNS. This folding produces ridges called convolutions (or gyri ; singular gyrus) and are separated either by shallow downfolds called sulci (singular ‘sulcus’) or deep downfolds called fissures.

Question 8

What is the longitudinal fissure?

Answer 8

The longitudinal fissure is the deepest fissure and almost separates the cerebrum into two halves ; the left and right cerebral hemispheres.

Question 9

What is the Corpus Callosum?

Answer 9

At the base of the longitudinal fissure is an area of white matter consisting of a large bundle of transverse fibres that join the two hemispheres. It is called the corpus callosum.

Question 10

List the 5 lobes of the cerebral hemispheres

Answer 10

• frontal
• temporal
• occipital
• parietal
• insula

Question 11

What are tracts?

Answer 11

Tracts are bundles of nerve fibres within the CNS. Bundles of nerve fibres outside the CNS are called nerves.

Question 12

What are three types of tracts that occur in white matter?

Answer 12

1 - tracts that connect various areas of the cortex within the same hemisphere.
2 - tracts that carry impulses between the left and right hemispheres.
3 - tracts that connect the cortex to other parts of the brain or to the spinal cord.

Question 13

Explain the function of the cerebrum

Answer 13

The cerebral cortex or cerebrum is involved in higher-order functions such as thinking, reasoning, memory, learning, and sense of responsibility. It is also concerned with perception of the senses and the initiation and control of voluntary muscle contraction.

Question 14

How have scientists found out what the cerebrum does? (5)

Answer 14

• studied brain waves and changes in voltage that occur in the cerebral cortex - which are detected by electrodes and recorded as an electroencephalogram (EEG)
• electrically stimulated certain areas and observed the responses
• examined changes in cerebral blood flow during different forms of mental and physical activity.
• observed the effects on people of brain damage and or disease
• experimented on other mammals

Question 15

What are the three types of functional area in the cortex?

Answer 15

• Sensory areas, which interpret impulses from receptors
• motor areas, which control muscular movements by sending impulses to muscles, especially for voluntary movement.
• association area, which are concerned with intellectual and emotional processes by interpreting information from senses and making them useful.

Question 16

What is the basal ganglia?

Answer 16

The basal ganglia consists of groups of nerve cell bodies associated with control of skeletal muscles. Nearly all of the impulses from our sense organs are carried to the cerebrum which has al the relevant information to initiate responses accordingly.

Question 17

How are memories stored in the cerebrum?

Answer 17

Memories are not stored in individual memory cells in the brain, they are pathways of nerve cells. When a memory is stored, new links are made between neurons or existing links are modified.

Question 18

What is the corpus callosum?

Answer 18

The corpus callosum is a wide band of nerve fibres that lies underneath the cerebrum at the base of the longitudinal fissure. Nerve fibres cross from one cerebral hemisphere to the other to allow them to communicate with eachother.

Question 19

What is the cerebellum?

Answer 19

The cerebellum lies under the rear part of the cerebrum and is the second largest part of the brain and its surface is folded into a series of parallel ridges. It exercises coordination of fine contractions of muscles resulting in smooth muscles and maintenance of posture and balance. It receives sensory information from the inner ear (for posture and balance) and from stretch receptors in skeletal muscles. Without the cerebellum our movements would be spasmodic, jerky and uncontrolled.

Question 20

What is the hypothalamus? (5)

Answer 20

The hypothalamus is an important organ that regulates secretions of the pituitary gland, body temperature, water balance, the autonomic nervous system and emotions.

Question 21

What is the medulla oblongata?

Answer 21

The MO is a continuation of the spinal cord and extends from just above the point where the spinal cord enters the skull. Many nerve fibres simply pass through the medulla but it also has an important role in automatically adjusting body functions. Basically, under the influence of the hypothalamus, the MO regulates the heart, breathing and diameter of blood vessels.

Question 22

What are the three centres that the medulla oblongata contains?

Answer 22

• the cardiac centre, which regulates the rate and force of heart beats.
• the respiratory centres, which control rate and depth of breathing.
• the vasomotor centre, which regulates the diameter of blood vessels.

Question 23

What is the spinal cord?

Answer 23

The spinal cord extends from the foremen magnum to the second lumbar vertebrae, which is about waist level. It is about 44cm in length.
It is heavily protected by the vertebral canal and the three meningeal layers. However, rather than the outmost meningeal layer, there is a space containing fat, connective tissue and blood vessels that serve as padding around the cord and allows it to bend.

Question 24

What is the foramen magnum?

Answer 24

The large opening at the base of the skull.

Question 25

What are the ascending tracts and descending tracts?

Answer 25

Ascending tracts are sensory axons that carry impulses upwards towards the brain.

Descending tracts contain motor axons that conduct impulses downwards away from the brain.

The second function of the spinal cord is to integrate certain reflexes. (Fast, automatic responses).